Aerodynamic generation of electric fields in turbulence laden with charged inertial particles

Abstract

Self-induced electricity, including lightning, is often observed in dusty atmospheres. However, the physical mechanisms leading to this phenomenon remain elusive as they are remarkably challenging to determine due to the high complexity of the multi-phase turbulent flows involved. Using a fast multi-pole method in direct numerical simulations of homogeneous turbulence laden with hundreds of millions of inertial particles, here we show that mesoscopic electric fields can be aerodynamically created in bi-disperse suspensions of oppositely charged particles. The generation mechanism is self-regulating and relies on turbulence preferentially concentrating particles of one sign in clouds while dispersing the others more uniformly. The resulting electric field varies over much larger length scales than both the mean inter-particle spacing and the size of the smallest eddies. Scaling analyses suggest that low ambient pressures, such as those prevailing in the atmosphere of Mars, increase the dynamical relevance of this aerodynamic mechanism for electrical breakdown.

Formation of decimeter-scale, long-lived elevated ionic conductivity regions in thunderclouds

“…18 and refs 19,20 ). Di Renzo and Urzay 21 introduced the aerodynamic mechanism of electric field generation in turbulence laden with bi-disperse suspensions of oppositely charged particles. The turbulence preferentially concentrates small particles in interstitial regions between vortices, where the strain rate is large.…”

“…The characteristic length associated with the resulting electric fields is much larger than the mean inter-particle distance and the smallest size of the turbulent eddies. 21 Although these turbulence-driven electric fields are expected to be small compared with the breakdown field in the atmosphere, they can lead to strong polarization of colliding (or nearly colliding) hydrometeors due to their high permittivity 22 and to initiation of small-scale discharges.…”

Quantifying the large-scale electrification equilibrium effects in dust storms using field observations at Qingtu Lake Observatory

“…Granular materials in dust events such as blowing sand, dust devils and dust storms, are frequently brought into contact or collision with each other, accumulating large amounts of electrical charge on their surfaces (Kamra, 1972;Rudge, 1913;Schmidt et al, 1998). The strong electrostatic forces exerted on dust particles, which are comparable to gravitational force, could considerably affect the motion of particles and facilitate the lifting of particles from the ground (Esposito et al, 2016;Harper et al, 2017;Kok and Renno, 2008;Schmidt et al, 1998;Zheng et al, 2003).…”

“…Measurements of electrical effects in dust events (especially dust storms) have been made for over 100 years, dating back to 1913 with the finding that the atmospheric vertical E-fields increased by 1-3 orders of magnitude and reversed their direction during dust storms (Rudge, 1913;Schmidt et al, 1998;Williams et al, 2009). However, owing to the difficulty in monitoring random dust events, only several tens of events are recorded in the literature (see Table 3 in Zheng, 2013, for details).…”

“…However, owing to the difficulty in monitoring random dust events, only several tens of events are recorded in the literature (see Table 3 in Zheng, 2013, for details). Previous studies are mainly concerned with the vertical profile of E-fields in the near-ground region and their influence on dust transport (e.g., Kamra, 1972;Rudge, 1913;Yair et al, 2016). The measurements showed that the vertical E-fields decrease with increasing height in the sub-meter region (e.g., Schmidt et al, 1998), but exhibit multi-layer properties in the region of up to 30 m height (Zhang et al, 2017).…”